Characterization of self-assembled monolayers of iron and cobalt octaalkylthiosubstituted phthalocyanines and their use in nitrite electrocatalytic oxidation

Cobalt and iron phenylthiosubstituted phthalocyanines have been deposited on Au electrode surfaces through the self-assembled monolayer (SAM) technique. The so formed layers were studied using voltammetric and impedance techniques. These SAMs blocked a number of Faradic processes and electrocatalyzed the oxidation of nitrite. The electrocatalytic parameters of the cobalt and iron phenylthiosubstituted phthalocyanines deposited on Au electrodes in nitrite solution were studied. Nitrite overpotentials which are lower than ever reported were obtained in this work for the iron phenylthiosubstituted phthalocyanines with very high stability.     

Quantitative risk assessment on the dietary exposure of Finnish children and adults to nitrite

Nitrite intake from the consumption of cured meat and tap water was estimated for Finnish children of 1, 3 and 6 years as well as Finnish adults of 25–74 years. Nitrite content in the foods was measured by capillary electrophoresis, and was then used together with individual food consumption data from the FINDIET 2007 and DIPP studies in a stochastic exposure assessment by a Monte Carlo Risk Assessment (MCRA) program. Nitrite intake from additive sources and tap water was assessed, and more than every 10th child between the ages 3 and 6 years was estimated to have a nitrite intake exceeding the acceptable daily intake (ADI) of nitrite. The high exposure levels were caused by frequent consumption of large portions of sausages, up to 350 g day^–1 or 750 g in 3 days, among the children. Median nitrite intake from cured meat was 0.016, 0.040, 0.033 and 0.005 mg kg^–1 body weight day^–1 for children of 1, 3 and 6 years and adults, respectively. Bayesian estimation was employed to determine safe consumption levels of sausages and cold cuts for children, and these results gave rise to new national food consumption advice.     

Parallel enzymatic and non-enzymatic formation of zinc protoporphyrin IX in pork

Zinc protoporphyrin is formed in pork homogenates in both enzymatic and non-enzymatic reactions. Ferrochelatase is active in formation of the highly fluorescent pigment known from Parma ham as demonstrated by inhibition with N-methylmesoporphyrin and by thermal inactivation. A non-enzymatic transmetallisation reaction, exchange of iron in myoglobin by zinc(II), is demonstrated by Pb(II) inhibition of zinc protoporphyrin formation at low Pb(II) concentrations, but promoted at higher Pb(II) concentrations. The non-enzymatic reaction is characterised as a slow bimolecular reaction between protoporphyrin IX and zinc(II) with a second-order rate constant of 0.63 l mol⁻¹ s⁻¹ at 35 °C and a high energy of activation of 98 kJ mol⁻¹ for acetone:water (3:1, v/v) as solvent. Zinc protoporphyrin formation is concluded to be thermodynamically controlled with a formation constant of 4 × 10⁵ M (35 °C, acetone:water (3:1)). An efficient inhibition of formation of zinc protoporphyrin by nitrite is related to myoglobin as substrate and involves both enzymatic and non-enzymatic reactions.     

基于以太网的亚硝酸根离子浓度智能检测仪表的研制

本文提出一种新颖的基于以太网亚硝酸根离子浓度检测系统,利用单片机MSP430作为检测仪表,以ARM9为核心处理器建立以太网网关,并在网关硬件平台上建立web服务器。用户可通过IE浏览器准确获得检测信息,从而实现NO2-离子浓度的远程监测。     

A new method for characterizing denitrifying phosphorus removal bacteria by using three different types of electron acceptors

This study investigated the characteristics of denitrifying phosphorus removal bacteria by using three different types of electron acceptors as well as the positive role of nitrite in phosphorus removal process. Denitrifying phosphorous removal bacteria was enriched under anaerobic-anoxic (A/A) condition. To understand A/A sludge better, sludge from two other sources were also studied. These include sludges obtained from a lab-scale anaerobic-anoxic-aerobic (A/A/O) system and a local sewage treatment plant. Three types of possible electron acceptors (oxygen, nitrate and nitrite) were examined for their roles in phosphorus uptake. The results obtained indicated that oxygen, nitrate and nitrite were able to act as electron acceptors successfully. This observation suggested that in addition to the two well-accepted groups of phosphorus removal bacteria (one can only utilize oxygen to take up phosphorus, P(O), while the other can use both oxygen and nitrate, P(ON)), a new group of phosphorus removal bacteria, P(ON(n)), which could use oxygen, nitrate or nitrite to take up phosphorus was identified. The relative population of these three types of bacteria could be calculated from results obtainable from phosphorus uptake batch experiments with either oxygen or nitrate or nitrite as electron acceptor. The results obtained in this study showed that A/A sludge had similar phosphorus removal performance as the A/A/O sludge. However, it has better denitrifying phosphorus removal capability, which was demonstrated by the relative population of the three groups of bacteria. The results also suggested that nitrite was not an inhibitor to phosphorus removal process. Instead, it is an alternative electron acceptor to oxygen or nitrate.     

Influence of nitrogen source on NDMA formation during chlorination of diuron

N-Nitrosodimethylamine (NDMA) is formed during chlorination of water containing the herbicide diuron (N′-(3,4-dichlorophenyl)-N,N-dimethylurea) but formation is greatly enhanced in the presence of ammonia (chloramination). Groundwater impacted by agricultural runoff may contain diuron and relatively high total nitrogen concentrations; this study examines the impact of the nitrogen form (ammonium, nitrite or nitrate) on NDMA formation during chlorination of such waters. NDMA formation during chlorination of diuron increased in the order nitrite < nitrate < ammonium for a given chlorine, nitrogen, and diuron dose. Formation of dichloramine seemed to fully explain enhanced NDMA formation in the presence of ammonium. Nitrate unexpectedly enhanced nitrosation of diuron derivatives to form NDMA compared to the cases of no added nitrogen or nitrite addition. Nitrite addition is less effective because it consumes more chlorine and produces intermediates that react rapidly with diuron and its aromatic byproducts. Differences between surface water and groundwater in nitrogen forms and concentrations and disinfection approaches suggest strategies to reduce NDMA formation should vary with drinking water source.     

一些果蔬对活性自由基和亚硝酸盐的消除作用

对29种新鲜水果和蔬菜的一般营养成分和过氧化物酶、过氧化氢酶活性以及对H_2O_2和NaNO_2的消除能力进行了测定。结果表明,在模拟胃液条件下,各种供试的新鲜果蔬对活性氧自由基和亚硝酸盐均具有不同程度的消除能力,其消除量与新鲜果蔬中的蛋白质含量呈极显著正相关。谷胱甘肽、还原型辅酶Ⅰ、维生素E、维生素C和半胱氨酸等还原性食品成分对NaNO_2和H_2O_2都有良好的线性消除关系。煮沸处理后,有机酸含量高的果蔬对NaNO_2和H_2O_2的消除能力增强,有机酸含量低时,其消除能力下降。提示果蔬对活性氧自由基和亚硝酸盐的消除能力取决于果蔬中还原性食品成分的种类、含量及其氧化还原特性。     

Interactive inhibition of meat spoilage and pathogenic bacteria by lysozyme,nisin and EDTA in the presence of nitrite and sodium chloride at 24 degrees C

To develop a nisin- and lysozyme-based antimicrobial treatment for use with processed ham and bologna, in vitro experiments were conducted to determine whether inhibition enhancing interactions occur between the antimicrobials lysozyme, chrisin (a commercial nisin preparation), EDTA, NaCl and NaNO₂. Inhibitory interactions were observed between a number of agents when used against specific pathogenic and spoilage bacteria. The observed interactions included lysozyme with EDTA (Enterococcus faecalis and Weissella viridescens), chrisin with EDTA (all Gram-positive organisms), EDTA with NaCl (Escherichia coli, Salmonella enterica serovar Typhimurium, Serratia grimesii), EDTA with nitrite (E. coli, Lactobacillus curvatus, Leuconostoc mesenteroides, Listeria monocytogenes, S. Typhimurium), chrisin with nitrite (Lc. mesenteroides, L. monocytogenes), and NaCl with nitrite (S. Typhimurium, Shewanella putrefaciens). Previous reports have described interactions between nisin with EDTA that resulted in enhanced antimicrobial effect against Gram-negative bacteria, or lysozyme with nisin against Gram-positive bacteria. These interactions were not observed in these experiments. We observed that unlike previous studies, these experiments were conducted on growing cells in nutrient broth, rather than under conditions of nutrient limitation. We propose that screening of antimicrobials for use in food systems in nutrient-deficient systems is inappropriate and that new protocols should be developed.     

Nitrous oxide generation in full-scale biological nutrient removal wastewater treatment plants

International guidance for estimating emissions of the greenhouse gas, nitrous oxide (N₂O), from biological nutrient removal (BNR) wastewater systems is presently inadequate. This study has adopted a rigorous mass balance approach to provide comprehensive N₂O emission and formation results from seven full-scale BNR wastewater treatment plants (WWTP). N₂O formation was shown to be always positive, yet highly variable across the seven plants. The calculated range of N₂O generation was 0.006-0.253 kgN₂O-N per kgN denitrified (average: 0.035 ± 0.027). This paper investigated the possible mechanisms of N₂O formation, rather than the locality of emissions. Higher N₂O generation was shown to generally correspond with higher nitrite concentrations, but with many competing and parallel nitrogen transformation reactions occurring, it was very difficult to clearly identify the predominant mechanism of N₂O production. The WWTPs designed and operated for low effluent TN (i.e. <10 mgN L⁻¹) had lower and less variable N₂O generation factors than plants that only achieved partial denitrification.